What are the advanced React Native interview questions and answers?

First of all, React Native is a popular mobile development framework using JavaScript. Developers widely use it to create apps for both Android and iOS platforms. Moreover, notable examples include Instagram, Facebook, and Skype.

Above all, if you want to land that React Native developer job of your dreams, you need to be well-prepared for your next interview with a top-notch resume on hand. Additionally, here are some top React Native interview questions and their sample answers for experienced developers.

10 Advanced React Native Interview Questions and Answers

1. What’s the main cause of the performance issues in React Native?

To begin with, the immense speed of each thread, namely the JS and Native threads, causes the performance issues in React Native. Therefore, bottlenecks in React Native apps generally occur when components from one thread are being passed onto another more than required. Overall, to avoid these issues, it’s crucial to keep the passes over the bridge to a minimum.

2. Memory leaks in React Native: describe what they are, including their main causes, and how they can be detected.

In terms of programming, it’s worth noting that JavaScript’s Garbage Collector plays a crucial role in managing memory allocation. Specifically, it’s responsible for identifying and cleaning up unneeded blocks of allocated memory. However, unused parts of the graph may be deallocated from memory.

On the other hand, such memory leaks can be prevented.

In React Native, it’s important to remember that each JavaScript module attaches to a root object. Moreover, this connection between modules and objects is crucial because it allows for seamless communication between different parts of your application. Also, modules in React Native (and others) declare variables that may prevent objects from being labeled as ‘garbage’ by the algorithm due to being kept in the main scope.

Common mistakes that lead to memory leaks in React Native apps include:

Closure scope leaks

Unreleased listeners/timers added in componentDidMount

Here’s how you can detect memory leaks for iOS and Android:

3. What is FlatList, and how is it better than ScrollView?

In React Native, developers frequently use the FlatList component to present large amounts of data in a scrolling list format. Furthermore, this is particularly common in news apps, where you can display a list of article summary cards on the home page. Moreover, it is more suitable for data lists that may change over time, unlike ScrollView. Additionally, FlatList component renders only visible items, providing a performance boost, unlike ScrollView, which creates all list items at once.

4. What is SSL Pinning in React Native?

First, SSL pinning (or certificate pinning) is a technique to enhance the security of SSL/TLS connections by linking a certificate or public key to a specific host. Moreover, this helps prevent man-in-the-middle (MITM) attacks by verifying the certificate or public key for establishing the connection.

5. What is a controlled and uncontrolled component in React Native?

To clarify the contrast, we can divide React Native components into two categories based on their internal state. First of all, some components, such as textInput, have a value attribute to display user input on the UI. These are uncontrolled components because React is not responsible for setting or changing their value.

However, if React manages the state of a component, it will become a controlled component. So, to make a component controlled, the developer assigns the component’s state as the value of control elements. And then, the developer adds a callback method to update the state on value change events. Overall, it is effective to use controlled components in React Native as it allows for better management of values and behaviour by React. Moreover, this gives the developer more control over the state of components.

6. What is rendering prop pattern in React Native?

The rendering prop pattern is a technique in React and React Native for sharing logic between components. Additionally, it allows a component (often referred to as the “container” or “higher-order” component) to pass a function that defines the markup to be rendered as a prop to another element (often referred to as the “child” or “presentational” component). Then, the child component this function, passing in any props that it receives to render the markup.

Above all, the main advantage of this pattern is that it allows for greater flexibility and reusability. Also, the container component can handle the logic and state management, while the child component can focus solely on rendering the markup. As a result, this allows for the child component to be used in multiple contexts with different logic and state.

7. How does virtual DOM work in React Native?

To optimize UI updates for web and mobile apps, React employs Virtual DOM. The virtual DOM represents the actual DOM, allowing React to compare the current state of the UI with the desired state. Overall, this comparison enables React to make only the necessary changes to the actual DOM, resulting in a faster and more efficient update process.

By this, React will first update the virtual DOM to reflect the new state when a component’s state or props change. After that, it will compare the virtual DOM with the previous version of the virtual DOM, and calculate the minimal set of changes required to update the actual DOM. As a result, we will call this process “Reconciliation”.

Once the calculation of the minimal set of changes is over, the virtual DOM updates the native views that are used to render the UI. Moreover, this allows React Native to efficiently update the UI of a mobile app while still taking advantage of the performance benefits of native code.

8. What are some the core components in React Native? Name the analogies of those components in web development.

There are several core components in React Native to build the user interface of a mobile app and some of the most commonly used components include:

9. What is setNativeProps?

setNativeProps is a method available in React Native that allows you to directly update the properties of a component’s corresponding native view. Furthermore, this can be useful in certain situations where you need to update the view without triggering a full re-render of the component.

Normally, when you update the state or props of a component, React will re-render the component and its children to reflect the new state. However, this can be slow and wasteful if you only need to make small updates to the view. On the other hand, by using setNativeProps, you can bypass the re-rendering process and update the native view directly, which can improve performance.

Overall, It’s worth noting that setNativeProps should be used sparingly and with caution, as it bypasses the normal react reconciliation process and it could cause unexpected behavior if not used correctly. As a result, you should only use setNativeProps when you are certain it will enhance the performance and won’t cause any inconsistencies.

10. What is the difference between FlatList and SectionList?

Both FlatList and SectionList are essential components in React Native, which provide optimal rendering of extensive data lists. In addition, they allow for efficient handling of complex data structures and layouts.

On the first hand, FlatList is a component for efficiently rendering large lists of items in a scrollable view. Mainly, it renders items lazily, meaning that it only renders the items that are currently visible on the screen, and unmounts items that are no longer visible.

On the other hand, SectionList is similar to FlatList, but it allows you to group items into sections. Each section can have a header and footer, and the items in the section are rendered using a FlatList.

In summary, FlatList is used to render a simple list of items, whereas SectionList is used to render a list of items grouped into sections.

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